Phenology ofSirodotia suecica(Batrachospermaceae, Rhodophyta) in a high-altitude stream in central Mexico

Abstract

SUMMARY The morphology and phenology of a monoecious population of Sirodotia suecica Kylin was evaluated seasonally in a central Mexican fifth-order high-altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s−1), low irradiance (75–263 µmol photons m−2 s−1) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. ‘Chantransia’ stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. However S. suecica was not common in the study region because it was restricted to particular microhabitat conditions.